JPH08297190A - Inspecting method for reactor fuel guide pin - Google Patents

Abstract

PURPOSE: To provide a method capable of accurately inspecting the structural integrity of a fuel guide pin including a screw clearance groove section and a screw section base end regardless of the coupling degree of the fuel guide pin into the insertion hole of a core plate. CONSTITUTION: The direct projection method from the outer periphery of a fuel guide pin 1 for detecting cracks on the pin neck lower section la' of the pin 1, the single reflection method from the outer periphery of the pin 1 for detecting cracks on a screw clearance groove section 1b' and a screw section base end 1c', and the incidence method from a core plate 3 are concurrently used. The shape echo generated when a shoulder section 1g near a screw section 1b is used as a reflection source is detected by the direct projection method, it is compared with the shape echo of a comparison test piece having the same shape and size as those of the fuel guide pin 1, and the pressure contact degree between the fuel guide pin 1 and the insertion hole 3a of the core plate 3 by cold fit is detected in advance. The detected result of the pressure contact degree is used for correcting the flaw detection sensitivity by selectively empolying the single reflection method and incidence method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inspection method for confirming the structural integrity of a fuel guide pin used for mounting a fuel assembly in a pressurized water reactor by using ultrasonic waves.

[0002]

2. Description of the Related Art The above-mentioned fuel guide pin is a reactor internal structure that serves to stably arrange and fix a fuel assembly, which is an energy source for nuclear power generation, at a predetermined position in a reactor vessel. It is an important member. In order to understand the inspection method according to the present invention, it is useful to know the internal structure of the reactor, the fuel assembly, etc., so that they will be briefly described first.

In the pressurized water reactor 10 shown in FIG.
A substantially cylindrical reactor core 12 is suspended in the reactor vessel 11, and internal reactor internals are arranged therein. A large number of fuel assemblies 14 constituting the in-core structure are arranged between the upper core plate 3 and the lower core plate 4. Further, as is well known, the lower core support plate 5, the lower core support column 6, the upper core support column 7, and the upper core support plate 8 are included in the internal structure.
A control rod cluster guide tube 9 is vertically provided above the upper core support plate 8.

FIG. 7 is a perspective view of the fuel assembly 14 described above, and FIGS. 8A to 8D are the fuel assembly 14 and the upper core plate 3 of FIG. 6 and the fuel assembly 14 and the lower portion. It shows the joint with the core plate 4, and the fuel assembly 14 is
Two (four in total) upper and lower fuel guide pins 1 and 2 attached to No. 4 on the diagonal line of the upper nozzle 15 and the lower nozzle 16 arranged at the upper end and the lower end of the fuel assembly 14, respectively. Position (see (B) and (C) of FIG. 8)
The presser spring 1 provided on the upper nozzle 15 is positioned by being inserted into the guide holes 17 and 18 formed in the upper nozzle 15.
It is fixed by being sandwiched between both core plates 3 and 4 via 9.

The above-mentioned upper and lower fuel guide pins 1 and 2
Has the structure shown in FIG. The upper fuel guide pin 1 and the lower fuel guide pin 2 have different lengths of the pin portions 1a and 2a protruding from the corresponding core plates 3 and 4, but the structures, dimensions, materials, etc. of other portions are substantially the same. Therefore, the upper fuel guide pin 1 will be representatively described below. However, this description below also applies to the lower fuel guide pins 2 mounted on the lower core plate 4, so that the terms "core plate" and "fuel guide pin" refer to "upper and lower core plates", respectively. As well as "upper and lower fuel guide pins".

The size of the fuel guide pin 1 is set to be slightly larger than that of the insertion hole 3a formed in the core plate 3. The fuel guide pin 1 is cooled and contracted, and then inserted into the insertion hole 3a. It is attached to the upper core plate 3 by a fixed cooling fit. The fuel guide pin 1 is also attached to the upper core plate 3 by screwing a nut 1c onto a small-diameter threaded portion 1b provided at the base end of the fuel guide pin 1. Further, the nut 1c is welded to the upper core plate 3 to prevent it from loosening. In FIG. 9, the area indicated by reference numeral 1d is the fitting portion, and the area indicated by reference numeral 1e is the anti-rotation welded portion.

As described above, the fuel guide pin 1 is fixed to the upper core plate 3 by taking double and triple safety measures. However, as the service life of the nuclear power plant becomes longer, there is a possibility that damage such as cracks may occur in the fuel guide pin 1 due to repeated small loads during operation and thermal stress. There is a possibility that the fixed state of the joint portion of the fuel guide pin 1 to the upper core plate 3 may be impaired.

FIG. 9 also shows a portion in which cracks preferentially occur, which is assumed from the stress acting on the fuel guide pin 1, and the propagation direction of the cracks. If a crack is generated in the fuel guide pin 1, a shoulder portion (so-called a pin neck lower portion) between the lower end of the pin portion 1a and the upper end of the fitting portion 1d 1
a ′, the screw relief groove portion 1b ′ between the lower end of the fitting portion 1d and the upper end of the screw portion 1b, and the base end 1c ′ of the screw portion 1b are represented by, for example, symbols F1, F2, and F3, respectively. A crack is expected to grow as shown in. Empirically, the crack F1 is caused by the insertion hole 3a of the core plate 3 in the fuel guide pin 1.
From the position corresponding to the upper edge of the pin 1a, the cracks F2 grow upward from the upper end of the screw escape groove 1b 'to the inside of the fitting portion 1d. F3
Has been found to grow downward from the upper end of the threaded portion 1b toward the inside of the threaded portion 1b.

In the unlikely event that a crack occurs at these joints, particularly at the above-mentioned site, and a crack develops and a pin portion 1a falls off, a fuel guide pin 1 Not only may the function be lost, but the dropped pin portion 1a may become foreign matter and enter the cooling water circulating in the furnace, and damage other members of the reactor internal structure. Therefore, in order to prevent the occurrence of the above-mentioned undesirable events,
There is a need for an inspection technique capable of early and accurately detecting a crack that may occur in the fuel guide pin 1.

As a non-destructive inspection method for the fuel guide pin,
Conventionally, a method using ultrasonic waves shown in FIG. 2 is known. This inspection method, which is referred to as the direct injection method, is such that the ultrasonic beam UB is obliquely directly incident from the probe 20 arranged on the outer peripheral surface of the pin, aiming at the vicinity of the shoulder portion 1a ′ of the fuel guide pin 1, If there is a crack, the reflected wave from it is probe 2
It is a method to detect cracks by receiving 0.
By rotating the probe 20 along the outer peripheral surface, the entire area of the annular shoulder can be inspected. Although this inspection method is a method in which the inspection range is limited to the shoulder portion 1a ′, which is called the so-called lower portion of the pin neck, or the vicinity thereof, the cracks F2, F3 ( 9) occurs and the screwing function is lost, the fuel guide pin 1 does not fall off as long as the cooling fitting function is maintained. Therefore, to that extent, it can be said that the soundness of the fuel guide pin 1 can be substantially confirmed by applying the present inspection method and inspecting the pin neck lower portion 1a ′.

However, in a nuclear power plant in operation, which is in progress of aging, in preparation for future long-life operation,
A thorough inspection based on a stricter safety evaluation is required for parts that may be damaged even a little. If, as shown in FIG. 9, a crack is generated in the screw relief groove portion 1b ′ or the screw portion base end 1c ′ and grows and breaks, if the cooling fitting is insufficient, it is in operation. There is a non-zero possibility that the fuel guide pin 1 will fall off the core plate 3 due to the vibration of the above. Further, if the locking welded portion 1e of the nut 1c is not sufficiently fixed, the probability that the nut 1c will fall out is low, but it cannot be denied at all.

As a general inspection method for detecting cracks in the screw escape groove portion 1b 'and the screw portion base end 1c' of the fuel guide pin 1, as shown in FIG. 3, as shown in FIG. A single reflection method of the acoustic beam UB is conceivable. In this inspection method, as shown in FIG. 3, the ultrasonic beam UB is obliquely incident from the outer peripheral surface of the pin portion of the fuel guide pin 1, and the boundary between the fitting portion 1d and the insertion hole 3a of the core plate 3 is made. Top reflection point 1
After being reflected once by f, the ultrasonic beam UB is guided to the screw escape groove portion 1b ′ and the screw portion base end 1c ′ (see FIG. 9), and the reflected wave from a crack that may exist in the portion is captured. This is a method of detecting cracks. Also in this inspection method, the entire circumference can be inspected by scanning the probe 20 around the pin.

[0013]

The above-mentioned single reflection method is
If the fuel guide pin 1 is a single unit, the screw relief groove 1
Although cracks in b ′ and the screw portion base end 1c ′ can be detected, in the state where the fuel guide pin 1 is assembled to the core plate 3 by cold fitting, since the reflection point 1f is in the fitting portion 5, There is a risk of overlooking cracks in the screw escape groove portion 1b 'and the screw portion base end 1c'. That is, since the relevant portion is in a state of being pressed against the upper core plate 3 by cooling fitting, as shown in FIG.
This is because the light will be transmitted to, and the expected reflection is unlikely to occur.

Therefore, as shown in FIG. 2, the inspection range is limited to the lower part 1a 'of the neck of the pin, and the direct injection method from the outer peripheral surface of the pin is used.
As shown in FIG. 3, the fuel guide pin 1 is combined with the single reflection method in which an ultrasonic beam is incident on the fitting portion from the outer peripheral surface of the pin.
Even if it is applied to the inspection of 1., it cannot be said that the inspection of the structural soundness of the fuel guide pin 1 including the screw relief groove portion 1b ′ and the screw portion base end 1c ′ is perfect. Therefore, in consideration of an unexpected possibility, it is strongly desired to develop a nondestructive inspection method capable of reliably detecting cracks generated in the screw relief groove portion 1b ′ to the screw portion base end 1c ′. Aims to provide such an inspection method.

[0015]

In order to achieve the above-mentioned object, the present invention provides a pin portion projecting from a core plate, and a pin portion connected to the pin portion and fixed to an insertion hole of the core plate by cold fitting. A fitting portion and a thread portion that is connected to the fitting portion via a screw relief groove portion and forms an annular shoulder portion between the fitting portion and the fitting portion, and a nut is screwed to the thread portion. Then, it is directed to a method for inspecting the structural integrity of a fuel guide pin for a nuclear reactor which is fastened to the core plate. In this inspection method, according to the present invention, a) a test piece produced by simulating the fuel guide pin is equivalently emitted from a probe at a first position on the outer peripheral surface of the pin portion of the test piece. Reflected ultrasonic beam toward a third position of the test piece at a second position on the outer peripheral surface of the fitting portion of the test piece,
The probe receives the reflected wave as the first echo signal,
b) With respect to the fuel guide pin mounted on the core plate, an ultrasonic beam emitted from the probe at the first position on the outer peripheral surface of the pin portion of the fuel guide pin The second position on the outer peripheral surface of the fitting portion is reflected toward the third position of the fuel guide pin, and the reflected wave is received by the probe as a second echo signal; Comparing the first echo signal with the second echo signal for the fuel guide pin, and d) for the fuel guide pin if the difference between the second echo signal and the first echo signal is less than or equal to a predetermined value. An ultrasonic beam emitted from a probe on the outer peripheral surface of the pin portion of the fuel guide pin, at a predetermined position on the outer peripheral surface of the fitting portion of the fuel guide pin, Reverse toward the screw relief groove or the base end of the screw. Then, the reflected wave is received by the probe, and a crack expected to occur at the screw relief groove portion or the base end of the screw portion is detected, and e) of the second echo signal with respect to the first echo signal. If the difference is equal to or more than a predetermined value, for the fuel guide pin, an ultrasonic beam is transmitted from the probe on the core plate through the fitting portion toward the screw relief groove portion or the base end of the screw portion. The probe is fired and the reflected wave is received by the probe to detect a crack expected to occur in the screw escape groove portion or the base end of the screw portion.

According to a preferred embodiment of the present invention, the fuel guide pin is provided with an artificial defect simulating a crack expected to occur in the screw relief groove portion of the fuel guide pin or a base end of the screw portion. Prepare a test piece manufactured in the same manner, and for the test piece, apply an ultrasonic beam emitted from the probe on the outer peripheral surface of the pin part to a predetermined position on the outer peripheral surface of the fitting part of the test piece. At the position, it is reflected toward the artificial defect of the test piece, the reflected wave is received by the probe, and a crack expected to occur at the screw escape groove portion of the fuel guide pin or the base end of the screw portion. The flaw detection sensitivity of the probe is set. From the probe on the outer peripheral surface of the pin portion of the fuel guide pin, an ultrasonic beam is emitted toward the vicinity of the boundary between the pin portion and the fitting portion, and a crack expected to occur near the boundary is generated. Is preferably detected. Also, preferably,
A test piece prepared in the same manner as the fuel guide pin, in which an artificial defect simulating a crack expected to occur is inserted near the boundary between the pin portion and the fitting portion of the fuel guide pin, is prepared, and the test is performed. Regarding the piece, an ultrasonic beam emitted from the probe on the outer peripheral surface of the pin portion is reflected toward the artificial defect near the boundary between the pin portion and the fitting portion of the test piece, and The reflected wave is received by the probe, and the flaw detection sensitivity of the probe with respect to a crack expected to occur near the boundary between the pin portion and the fitting portion of the fuel guide pin is set.
Further, based on the difference between the second echo signal and the first echo signal, the flaw detection sensitivity of the probe regarding a crack that is predicted to occur in the thread relief groove portion of the fuel guide pin or the base end of the thread portion. It is advantageous to correct

[0017]

In order to effectively detect a crack in the ultrasonic flaw detection method, that is, to effectively receive a reflected wave (echo) from the crack surface, an ultrasonic beam can be applied to the crack surface. It is important to select a flaw detection method with incident conditions that are as orthogonal as possible. From this point of view, the single reflection method of the ultrasonic beam from the outer peripheral surface of the pin shown in FIG. 3 is used when the pressure contact force (contact pressure) between the fuel guide pin and the insertion hole of the core plate is weak. As a method of detecting a crack at the base end (the relevant portion), the incident condition is close to ideal.

However, as the surface pressure of the part increases, the ultrasonic beam reflection in the part becomes weaker, and the advantage of the single reflection method is lost when the surface pressure is strong. The method of injecting the ultrasonic beam from the core plate adopted according to the present invention is effective in such a state of strong surface pressure. FIG. 11 shows the relationship between the surface pressure of the fuel guide pin and the insertion hole of the core plate, and the reflected wave and the transmitted wave at the relevant portion. From this figure, it can be seen that the surface pressure at the relevant portion increases as the surface pressure increases. It can be seen that while the reflected wave becomes weaker, the transmitted wave becomes stronger.

Therefore, as shown in FIG. 4, the ultrasonic beam incident from the core plate is transmitted through the fitting portion of the fuel guide pin and guided to the corresponding portion of the fuel guide pin. It is effective in some cases to send and receive ultrasonic beams by the child. In this way, the success or failure of the single reflection method and the injection method for detecting cracks in the screw escape groove portion and the base end of the screw portion depends on the surface pressure between the fuel guide pin and the insertion hole of the core plate, Have a relationship. Therefore, in detecting flaws using both methods, it is important to predict the state of the surface pressure involved in the reflection and transmission of the ultrasonic beam at the relevant portion and use the appropriate method properly.

Further, in order to improve the inspection accuracy, the method according to claim 5 is provided.
As described above, it is important to correct the loss in reflection and transmission of ultrasonic waves at the relevant portion and perform flaw detection. As a reflection source (the third position of the fuel guide pin) for monitoring the degree of loss of reflection and transmission of ultrasonic waves at the relevant portion, there is a shoulder portion near the screw portion shown in FIG. Since the reflection source is close to the screw part of the inspection site, as can be seen by comparing FIG. 3 and FIG. 5, by displacing the incident point of the ultrasonic beam upward, the echo of the part can be detected. .

As the inspection procedure, first, as in claim 2, after the direct irradiation method from the outer peripheral surface of the pin portion is applied, the vicinity of the boundary between the pin portion and the fitting portion, that is, the lower portion of the pin neck is inspected. ,
Move on to the inspection of the screw relief groove and the base of the screw. When inspecting the screw relief groove portion and the screw portion base end, an echo from the shoulder portion near the screw portion as a reflection source is examined by using the single reflection method from the outer peripheral surface of the pin portion. As a result, if the echo is less reduced than that of the comparative test piece (state of the fuel guide pin alone), it is determined that the surface pressure of the fitting portion of the fuel guide pin is low. In this case, the single reflection method from the outer peripheral surface of the pin portion is selected as the inspection method for the screw relief groove portion and the screw portion base end. Further, in this case, as described above, the influence of the reflection loss of the surface pressure at the fitting portion of the fuel guide pin is corrected by increasing the flaw detection sensitivity according to the situation of the echo.

On the other hand, in the examination result of the echo of the ultrasonic beam using the single reflection method from the outer peripheral surface of the pin portion, if the decrease is large as compared with that of the comparative test piece (the state of the fuel guide pin alone), It is determined that the surface pressure at the fitting portion of the fuel guide pin is high. In this case, an ultrasonic beam injection method from the core plate using the ultrasonic transmission phenomenon at the relevant part will be established, so this injection method is used for the screw escape groove and the screw end base inspection method. To be selected as. In addition, in the result of investigation of the echo using the single reflection method from the outer peripheral surface of the pin portion, if it is determined that the intermediate pressure contact state is obtained, the single reflection method and the incident method may be used together. .

In both the single reflection method and the incident method, the probe is circulated around the pin to detect a reflected wave (echo) due to the presence of damage such as a crack and set a threshold value. The entire circumference may be inspected by detecting this. As mentioned above, three methods can be used together, or different methods can be used according to the state of the surface pressure at the fitting part.
By correcting the flaw detection sensitivity, a highly reliable inspection of the fuel guide pin can be realized.

[0024]

Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings. In the drawings, the same reference numerals indicate the same or corresponding parts. FIG. 1 is a block diagram showing the procedure of a method for inspecting a fuel guide pin according to an embodiment of the present invention. First, the direct injection method from the outer peripheral surface of the pin described with reference to FIG.
The inspection of a'is performed (steps 100 and 101). That is, in FIGS. 2 and 9, the ultrasonic beam UB is obliquely directly incident from the probe 20 arranged on the outer peripheral surface of the pin toward the vicinity of the shoulder portion 1a ′ of the fuel guide pin 1 and a crack is present. If so, the reflected wave from the probe 20 is received by the probe 20 to detect the crack. Although not shown, the probe 20 is connected to a control device which may be a computer and an appropriate driving means, and the reception signal thereof is transmitted to the control device. Further, the probe 20 can be circulated along the outer peripheral surface of the pin by the driving means, and the inspection of the entire area of the annular shoulder portion 1a ′ is performed along with the circling.

Before starting this inspection, the probe 20 is made of an artificial defect which is made of the same material and has the same shape as the fuel guide pin 1 to be inspected and which simulates a crack that is expected to occur in the lower portion of the pin neck. Using the inserted contrast test piece (not shown),
The first predetermined flaw detection sensitivity is set, and this first predetermined flaw detection sensitivity (threshold value) is input to the control device in advance. The shape echo signal representing a crack or the like detected by the probe 20 is compared with a threshold value in the control device, and the soundness of the relevant part is determined by whether or not an echo equal to or larger than the threshold value is detected ( Step 102). If there is an echo equal to or more than the threshold value, it is judged that the lower portion 1a 'of the pin neck is damaged (step 102a), and the inspection is completed. If there is no echo above the threshold value, another part is examined.

That is, the process proceeds to the inspection of the screw relief groove portion 1b 'and the base end 1c' of the screw portion 1b by the single reflection method from the outer peripheral surface of the pin (step 103). First, the fitting portion 1 of the fuel guide pin 1 is formed by using the single reflection method from the outer peripheral surface of the pin shown in FIG.
The degree of press contact at d is investigated, but before that, as for the probe 20, as in the case of the direct injection method described above, the escape groove portion 1 of the screw is made of the same material and shape as the fuel guide pin.
The second predetermined flaw detection sensitivity is set in advance by using a comparative test piece (state of a single fuel pin) in which an artificial defect simulating a crack that is expected to occur is inserted in b ′ and the screw portion base end 1c ′. deep. At this time, as shown in FIG. 5, with respect to the comparative test piece, the height of the shape echo having a portion corresponding to the shoulder 1g of the screw portion 1b as a reflection source is grasped and input to the control device (step 104). .

After setting the second predetermined flaw detection sensitivity, the screw portion 1
The ultrasonic beam of the probe 20 is scanned aiming at the shoulder portion 1g of b, and the height of the shape echo of the portion is examined (step 10).
5). If the shape echo height is a specific value or more (specifically, compared with the height of the shape echo described above for the comparative test piece when setting the second predetermined flaw detection sensitivity, for example, 1/2 to The surface pressure between the fitting portion 1d and the insertion hole 3a is low to the extent that there is no large decrease of 1/3). In that case, the single reflection method from the pin outer peripheral surface is performed by the screw escape groove portion 1b ′.
Also, the single reflection method is selected as an inspection method for the base end 1c 'of the screw portion 1b, and the single reflection method is selected as an inspection method for the screw escape groove portion 1b' and the base end 1c 'of the screw portion 1b (step 106).

In that case, the height of the shape echo is compared with the height of the shape echo of the contrast test piece measured in step 104 when the sensitivity is set (step 10).
7) By using the difference value as a threshold value in addition to the above-described second predetermined flaw detection sensitivity (step 108), the reflection loss corrected by the contact pressure between the fuel guide pin 1 and the insertion hole 3a is corrected. Can be realized.

After the flaw detection sensitivity is corrected as described above, the screw escape groove portion 1b 'and the base end 1c' of the screw portion 1b are inspected by the single reflection method (step 109). That is, in FIGS. 3 and 9, the ultrasonic beam UB is obliquely incident from the outer peripheral surface of the pin portion of the fuel guide pin 1, and the reflection on the boundary between the fitting portion 1d and the insertion hole 3a of the core plate 3 is reflected. After being reflected once at the point 1f, the screw escape groove portion 1b ', the screw portion base end 1
A crack is detected by guiding an ultrasonic beam to c ′ (see FIG. 9) and capturing a reflected wave from a crack that may be present in the relevant portion. Also in the single reflection method, the entire circumference can be inspected by rotating the probe 20 around the pin in the same manner as the direct irradiation method.

The echo signal representing the detected crack is sent to a control device (not shown), and is compared with a threshold value which is the corrected second predetermined flaw detection sensitivity. As a result, echoes above the threshold value are detected. The soundness of the part is determined by whether or not a signal is detected (step 110). That is, if there is no echo above the threshold, it is judged that the screw relief groove portion 1b ′ and the base end 1c ′ of the screw portion 1b are sound (step 111). It is determined that the escape groove portion 1b 'and the base end 1c' of the screw portion 1b are damaged (step 112), and the inspection ends.

On the other hand, when the height of the shape echo is greatly reduced (about ⅓) as compared with the height of the shape echo of the comparative test piece when the sensitivity is set, the fuel guide pin 1 and the insertion hole 3a. Since the surface pressure at the pressure contact portion between the two becomes high, and the above-mentioned single reflection method from the outer peripheral surface of the pin cannot be established as an inspection method for the screw relief groove portion 1b ′ and the base end 1c ′ of the screw portion 1b, on the other hand, from the core plate The injection method described later will be established. That is, when the echo height is greatly reduced, even if the single reflection method from the pin outer peripheral surface is simply performed in addition to the sensitivity correction, noise increases and a small crack cannot be detected at all. The injection method from the core plate utilizing the transmission of the ultrasonic wave is selected as the inspection method for the screw relief groove portion 1b 'and the base end 1c' of the screw portion 1b.

In the injection method from the core plate, first, the probe 20 arranged on the core plate 3 is aimed at the shoulder portion 1g of the screw portion 1b to detect flaws, and the shape of the relevant portion of the inspection object itself is detected. Using echo, the third predetermined flaw detection sensitivity is set as a threshold value (step 113). By this method, it is possible to realize the inspection in which the transmission loss of the ultrasonic beam UB related to the surface pressure of the pressure contact portion is corrected.

After the flaw detection sensitivity is set, the ultrasonic beam UB is emitted from the probe 20 toward the screw relief groove portion 1b 'and the base end 1c' of the screw portion 1b, and the inspection is performed (step 114). As a result, the soundness of the part is judged (steps 115, 116, 117) depending on whether or not the echo above the threshold value is detected (steps 115, 116, 117) and the inspection is completed.

In the single reflection method from the outer peripheral surface of the pin, the height of the shape echo having the shoulder 1g of the screw portion 1b as a reflection source is about 1/4 to 1/3 of the shape echo of the comparative test piece. In such a case, it is preferable to inspect the screw escape groove portion 1b ′ and the screw portion base end 1c ′ by using the single reflection method from the outer peripheral surface and the incidence method from the core plate.

[0035]

According to the present invention having the above-mentioned structure, the following effects can be obtained, and the inspection of the fuel guide pin of the pressurized water reactor can be realized with higher reliability than the conventional method. 1. By using the one-time reflection method and the injection method from the core plate together, cracks in the screw escape groove and the base end of the screw can be detected. At that time, using the single reflection method from the outer peripheral surface of the pin,
For each of the fuel guide pin and the test piece, the shape echo that uses the shoulder near the screw as the reflection source is investigated, and the flaw detection method is selected based on the result. It is possible to carry out the inspection by an appropriate method according to the pressure contact state due to the cold fitting (claim 1). 2. Further, the inspection accuracy can be improved by setting the flaw detection sensitivity of the probe (claims 2 and 4). 3. Furthermore, if the direct injection method from the outer peripheral surface of the pin is also used, it is possible to inspect almost the entire area of the fuel guide pin in which a crack is predicted to occur, and the reliability of the fuel guide pin is improved (claim 3). 4. In the one-time reflection method from the outer peripheral surface of the pin, the result of the echo investigation is fed back to the correction of the flaw detection sensitivity, so that the influence of the reflection loss in the relevant portion related to the pressure contact state due to the cold fitting can be corrected (claim 5).

[Brief description of drawings]

FIG. 1 is a flow chart of a method for inspecting a reactor fuel guide pin according to an embodiment of the present invention.

FIG. 2 is an explanatory view of a direct injection method for detecting cracks under the neck of a fuel guide pin.

FIG. 3 is an explanatory diagram of an injection method from a pin outer peripheral surface for the purpose of detecting cracks in a screw clearance groove portion and a screw portion base end of a fuel guide pin.

FIG. 4 is an explanatory diagram of a reflection method from a core plate for the purpose of detecting cracks in a screw escape groove portion and a screw portion base end of a fuel guide pin.

FIG. 5 is an explanatory diagram of detection of a shape echo by the above-described injection method for the purpose of detecting cracks in a screw relief groove portion and a screw portion base end.

FIG. 6 is a vertical cross-sectional view showing the overall configuration of a pressurized water reactor.

7 is one perspective view of a fuel assembly used in the pressurized water reactor of FIG. 6. FIG.

8A to 8D are functional explanatory views of a fuel guide pin to be inspected used for mounting the fuel assembly of FIG. 7.

9 is a cross-sectional view showing the structure of the fuel guide pin of FIG. 8 with a portion where damage is expected to occur and partially broken.

FIG. 10 is an explanatory view of the operation of the reflection method for detecting cracks in the threaded portion of the fuel guide pin when the contact surface pressure between the fuel guide pin and the insertion hole formed in the core plate is high.

FIG. 11 is a diagram showing the relationship between the contact surface pressure of the fuel guide pin and the insertion hole of the core plate and the intensity of reflection and transmission of the ultrasonic beam at the relevant portion.

[Explanation of symbols]

1 ... Upper fuel guide pin (fuel guide pin), 1a ... Pin part, 1a '... Boundary between pin part and fitting part (bottom of pin neck),
1b ... screw part, 1b '... screw relief groove part, 1c ... nut,
1c '... screw base end, 1d ... fitting part, 1f ... reflection point (second position), 1g ... shoulder (third position), 2 ... lower fuel guide pin (fuel guide pin), 3 ... upper core Plate (core plate), 3
a ... insertion hole, 4 ... lower core plate (core plate), 20 ... probe, F1, F2, F3 ... crack, UB ... ultrasonic beam.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Takanobu Yamashita 1-1 1-1 Wadazaki-cho, Hyogo-ku, Kobe-shi, Hyogo Prefecture Mitsubishi Heavy Industries, Ltd. Kobe Shipyard (72) Inventor Koji Tanaka Hyogo-ku, Kobe-shi, Hyogo 1-1-1 Wadazakicho Mitsubishi Heavy Industries Ltd. Kobe Shipyard

Claims (5)

[Claims] 1. A pin portion protruding from a core plate, a fitting portion connected to the pin portion and fixed to an insertion hole of the core plate by cold fitting, and a screw escape groove portion in the fitting portion. Of a fuel guide pin for a nuclear reactor, which has a threaded portion that is connected to the fitting portion and forms an annular shoulder portion with the fitting portion, and a nut is screwed to the threaded portion and tightened to the core plate. A method for inspecting structural integrity, comprising: a) a probe located at a first position on an outer peripheral surface of a pin portion of a test piece that is manufactured by simulating the fuel guide pin. The ultrasonic beam emitted from the child is reflected toward the third position of the test piece at the second position on the outer peripheral surface of the fitting portion of the test piece, and the reflected wave is first echoed by the probe. B) with respect to the fuel guide pin mounted on the core plate, The ultrasonic beam emitted from the probe at the first position on the outer peripheral surface of the pin portion is moved to the third position of the fuel guide pin at the second position on the outer peripheral surface of the fitting portion of the fuel guide pin. Reflected toward the position and received by the probe as a second echo signal, and c) comparing the first echo signal for the test piece with the second echo signal for the fuel guide pin. D) If the difference between the second echo signal and the first echo signal is less than or equal to a predetermined value, the fuel guide pin is fired from a probe on the outer peripheral surface of the pin portion of the fuel guide pin. Reflected ultrasonic beam toward a base end of the screw escape groove portion or the screw portion of the fuel guide pin at a predetermined position on the outer peripheral surface of the fitting portion of the fuel guide pin,
The probe receives the reflected wave to detect a crack expected to occur at the screw escape groove portion or the base end of the screw portion, and e) the difference between the second echo signal and the first echo signal is If the value is equal to or more than a predetermined value, an ultrasonic beam is emitted to the fuel guide pin from the probe on the core plate through the fitting portion toward the screw relief groove portion or the base end of the screw portion. A method for inspecting a reactor fuel guide pin, wherein a reflected wave is received by the probe to detect a crack expected to occur in the screw relief groove portion or the base end of the screw portion. 2. A test piece manufactured in the same manner as the fuel guide pin, in which an artificial defect simulating a crack that is predicted to occur is inserted in the screw relief groove portion of the fuel guide pin or the base end of the screw portion. For the test piece, an ultrasonic beam emitted from the probe on the outer peripheral surface of the pin portion is used to generate the artificial beam of the test piece at a predetermined position on the outer peripheral surface of the fitting portion of the test piece. The flaw detection sensitivity of the probe with respect to a crack expected to occur at the screw relief groove portion of the fuel guide pin or the base end of the screw portion by reflecting the wave toward the defect and receiving the reflected wave at the probe. The inspection method according to claim 1, wherein 3. An ultrasonic beam is emitted from the probe on the outer peripheral surface of the pin portion of the fuel guide pin toward the vicinity of the boundary between the pin portion and the fitting portion, and is generated near the boundary. The inspection method according to claim 1, wherein a crack that is predicted to be detected is detected. 4. A test piece manufactured in the same manner as the fuel guide pin, in which an artificial defect simulating a crack that is predicted to occur is inserted near the boundary between the pin portion and the fitting portion of the fuel guide pin. For the test piece, an ultrasonic beam emitted from the probe on the outer peripheral surface of the pin portion is directed toward the artificial defect near the boundary between the pin portion and the fitting portion of the test piece. Reflected by the probe, and the reflected wave is received by the probe to set the flaw detection sensitivity of the probe for a crack expected to occur near the boundary between the pin portion and the fitting portion of the fuel guide pin. The inspection method according to claim 3. 5. The probe relating to a crack that is predicted to occur in the screw escape groove portion or the base end of the screw portion of the fuel guide pin based on a difference between the second echo signal and the first echo signal. The inspection method according to claim 2, wherein the flaw detection sensitivity is corrected.